Answers test examination

Evaluation of question 21:

Reading Figure C at 90 kV and 3 mm aluminum
–› 0.08 mSv/mA·s at 1 meter
The mAs value = 6 mA × 0.15 s = 0.9 mA·s
The equivalent dose at 1 meter
–› 0.08 mSv/mA·s × 0.9 mA·s = 0.07 mSv
The equivalent dose at 25 cm = 0.25 m
–› 0.07 mSv × (1 m / 0.25 m)² = 1.1 mSv

Evaluation of question 22:

Formula effective dose bystander
–› E (in μSv/y) = [DAP (in mGy·cm²) / 200] × N × T / r²
Reading Figure B at 90 kV and 10 mm glass
–› T = 0.34
Inserting in formula
–› E = (800 mGy∙cm² / 200) × 1200 × 0.34 / (1.5 m)² = 725 µSv/y = 0.73 mSv/y
Limit is 0.1 mSv/y
–› limit is widely exceeded

Evaluation of question 23:

Entrance dose = 1100 mGy·cm² / (18 cm × 10 cm) = 6.1 mGy
Total tissue weighting factor
–› w_T = 0.04 + 0.01 + 0.009 = 0.059
Effective dose of patient
–› E_patient = 1 Sv/Gy × 0.059 × 6.1 mGy = 0.36 mSv
Radiation weighting factor = w_X-ray = 1 Sv/Gy missing –› 0.5 pt deduction
H_scatter (in μSv) = DAP (in mGy·cm²) / 200 = 1100 mGy·cm² / 200 = 5.5 μSv op 1 m
Effective dose of dental surgeon
–› E_surgeon = 5.5 μSv × (1 m / 3 m)² = 0.6 μSv

Evaluation of question 24:

Formula effective dose bystander in case of intraoral device
–› E (in μSv/y) = 1 μSv × N × T / r²
Reading Figure E at 70 kV and 12.5 mm plaster
–› T = 0.4
Inserting in formula
–› E = 1 μSv × 2000 × 0.4 / (2.5 m)² = 128 μSv
Formula effective dose bystander in case of CBCT scanner
–› E (in μSv/y) = [DAP (in mGy·cm²) / 200] × N × T / r²
Reading Figuur E at 90 kV and 12.5 mm plaster
–› T = 0.6
Inserting in formula
–› E = (600 mGy·cm² / 200) × 300 × 0.6 / (1.5 m)² = 240 μSv/y
Total annual effective dose = 128 + 240 = 368 μSv/y